Method of manufacturing nano-scale LED electrode assembly comprising selective metal ohmic layer

ABSTRACT

A method of manufacturing a nano-scale LED electrode assembly including a selective metal ohmic layer is disclosed. Specifically, the method can be useful in increasing conductivity between a nano-scale LED device and electrodes and also reducing contact resistance therebetween by depositing a conductive material in a region in which the nano-scale LED device comes in contact with the electrodes so as to improve the contact between the nano-scale LED device and the electrodes, thereby further improving light extraction efficiency of the nano-scale LED device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0161300, filed on Nov. 17, 2015, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a method of manufacturing a nano-scaleLED electrode assembly including a selective metal ohmic layer, and moreparticularly, to a method of manufacturing a nano-scale LED electrodeassembly including a selective metal ohmic layer, which is capable ofincreasing conductivity between electrodes and a nano-scale LED deviceand also reducing contact resistance therebetween.

2. Discussion of Related Art

The development of light emitting diodes (LEDs) has been facilitatedsince 1992 when Nakamura et al. from Nichia Chemical Corporation (Japan)succeeded in fusing a high-quality single-crystal gallium nitride (GaN)semiconductor by applying a low-temperature GaN compound buffer layer.An LED is a semiconductor device having a structure in which n-typesemiconductor crystals having a plurality of carriers, i.e., electrons,and p-type semiconductor crystals having a plurality of carriers, i.e.,holes, are joined using the characteristics of a compound semiconductor,that is, a semiconductor device that converts an electrical signal intolight having a wavelength band at a desired region to emit the light.

Such an LED semiconductor is called a revolution of light as a greenmaterial because the LED semiconductor has very low energy consumptiondue to high light conversion efficiency, has a semi-permanent lifespanand is environmentally friendly. With the current development ofcompound semiconductor technology, red, orange, green, blue, and whiteLEDs having high brightness have been developed. Also, the LEDs havebeen applied to various fields such as traffic lights, mobile phones,headlights for vehicles, outdoor electronic display boards, LEDbacklight units (BLUs), and indoor/outdoor lightings, and thus researchon the LEDs is still being actively conducted. In particular, aGaN-based compound semiconductor material having a wide band gap is amaterial that has been used to manufacture LED semiconductors which emitgreen and blue light and ultraviolet rays. Since it is possible tomanufacture white LED devices using blue LED devices, much research onsuch a manufacturing method has been conducted.

Owing to the application of the LED semiconductor to various fields andthe research on the LED semiconductor, LED semiconductors having highpower output are also needed, and thus it is very important to improveefficiency of the LED semiconductor. However, there are severaldifficulties in manufacturing the blue LED device having high efficiencyand high power output.

The difficulties in improving the efficiency of the blue LED device mayresult from the difficulty in a manufacturing process and a highrefractive index of the manufactured LED between the GaN-basedsemiconductor and the atmosphere.

First, the difficulty in the manufacturing process may be due to thedifficulty in manufacturing a substrate having the same lattice constantas the GaN-based semiconductor. A GaN epitaxial layer formed on thesubstrate has a drawback in that many defects may occur when the latticeconstant of the epitaxial layer is significantly mismatched with that ofthe substrate, resulting in lowered efficiency and performance.

Next, light emitted from an active layer of the LED does not escape tothe outside but is totally reflected to the inside of the LED due to thehigh refractive index of the manufactured blue LED between the GaN-basedsemiconductor and the atmosphere. Such totally reflected light may bereabsorbed inside of the LED, resulting in deteriorated efficiency ofthe LED. Such efficiency may be referred to light extraction efficiencyof an LED device. To solve the above problems, much research is beingconducted.

Meanwhile, to make use of the LED device in lightings, displays, and thelike, an LED device and an electrode for applying power to the LEDdevice are required. Also, research on an arrangement of the LED deviceand two different electrodes in connection with an application purpose,a decrease in a space occupied by the electrodes, or a manufacturingmethod has been variously conducted.

Research on the arrangement of the LED device and the electrodes may beclassified into a method of growing an LED device on electrodes and amethod of separately growing an LED device and arranging the LED deviceon electrodes.

First, in research on growing the LED device on the electrodes, there isa bottom-up method in which the LED device and the electrodes are formedand arranged at the same time through a series of manufacturingprocesses using a method which includes forming a lower electrode on asubstrate in the form of a thin film, and sequentially stacking ann-type semiconductor layer, an active layer, a p-type semiconductorlayer, and an upper electrode on the lower electrode and etching thestacked layers, or etching the previously stacked layers prior tostacking the upper electrode and then stacking the upper electrode.

Next, the method of separately and independently growing an LED deviceand arranging the LED device on electrodes is a method includingindependently growing LED devices using a separate process, and thenarranging the manufactured LED devices on patterned electrodes one byone.

The former method has a problem in that it is very difficult to grow ahigh-crystalline/high-efficiency thin film and an LED device in acrystallographic aspect, and the latter has a problem in that lightemitting efficiency may be deteriorated due to low light extractionefficiency.

Also, the latter method has a problem in that a three-dimensional (3D)LED device may be erected and connected to electrodes in case of theconventional LED devices, but it is very difficult to erect a 3D LEDdevice on electrodes when the LED device is an LED device having anano-scale size. Korean Patent Application No. 2011-0040174 filed by theinventor of this application discloses a coupling linker for promotingcoupling of a nano-scale LED device having a nano-scale size toelectrodes in a state in which the LED device is coupled to theelectrodes in a 3D erect state. In fact, however, it is very difficultto couple the nano-scale LED device to the electrodes in the 3D erectstate when utilizing nano-scale electrodes.

Further, the separately manufactured LED devices have to be arranged oneby one on the patterned electrodes. However, when the size of the LEDdevices is very small (e.g., a nano-scale size), the LED devices havedrawbacks in that it is very difficult to arrange the LED devices on twodifferent nano-scale electrodes within a desired range, and defectsoften occur due to electrical short circuits between the electrodes andthe nano-scale LEDs even when the LED devices are disposed on the twodifferent nano-scale electrodes, which makes it impossible to realize adesired electrode assembly.

Also, Korean Patent Application No. 2010-0042321 discloses a structureof an address electrode line for LED modules and a method ofmanufacturing the same. In case of this application, a lower electrodeis formed on a substrate in the form of a thin film, and an insulationlayer and an upper electrode are sequentially stacked on the lowerelectrode, and then etched to manufacture an electrode line. Then, anLED chip is mounted on the upper electrode. However, when the mountedLED chip has a nano-scale size, it is very difficult to accurately mountthe 3D LED chip on the upper electrode in an erect state. Even when theLED chip is mounted on the upper electrode, it is also difficult toconnect the mounted LED chip having the nano size to the lowerelectrode.

Further, when the separately mounted LED devices are disposed on theelectrodes to apply power to the electrodes, contact resistance betweenthe LED devices and the electrodes occurs, resulting in degraded lightextraction efficiency.

SUMMARY OF THE INVENTION

To solve the above problems, the present invention is directed to amethod of manufacturing a nano-scale LED electrode assembly including aselective metal ohmic layer, which is capable of increasing conductivitybetween electrodes and an LED device and also reducing contactresistance therebetween by depositing a conductive material in a regionin which the LED device comes in contact with the electrodes so as toimprove the contact between the LED device and the electrodes.

According to an aspect of the present invention, there is provided amethod of manufacturing a nano-scale LED electrode assembly including aselective metal ohmic layer, which includes (1) manufacturing anano-scale LED electrode assembly by self-aligning nano-scale LEDdevices on an electrode line including first and second electrodes whichare formed on a base substrate to be spaced apart from each other; and(2) forming a metal ohmic layer on the nano-scale LED electrode assemblyby immersing the nano-scale LED electrode assembly in an electroplatingsolution and applying a power source to one of the first and secondelectrodes of the nano-scale LED electrode assembly to perform anelectroplating process for a plating time (T₁) of 1 to 300 minutes.

According to one preferred embodiment of the present invention, themethod may further include (3) forming a metal ohmic layer on thenano-scale LED electrode assembly by applying a power source to theother electrode, to which the power source is not applied in operation2, to perform an electroplating process for a plating time (T₂)satisfying the following Mathematical Expression 1:1 Minute≤Plating time T ₂ ≤T ₁  [Mathematical Expression 1]

wherein T₁ represents a plating time required for the electroplatingprocess in operation 2.

According to another preferred embodiment of the present invention, thepower source in operation 2 may be applied in the form of pulse waveshaving a voltage of −0.2 to −1.0 V, and the power source of the pulsewaves may be applied for 0.05 to 30 seconds and paused for 0.05 to 30seconds.

According to still another preferred embodiment of the presentinvention, the power source in operation 3 may be applied in the form ofpulse waves having a voltage of −0.2 to −1.0 V, and the power source ofthe pulse waves may be applied for 0.05 to 30 seconds and paused for0.05 to 30 seconds.

According to yet another preferred embodiment of the present invention,the electroplating solution may include at least one metal precursorselected from the group consisting of a gold precursor, a silverprecursor, a copper precursor, and a platinum precursor.

According to yet another preferred embodiment of the present invention,the electroplating solution may include the metal precursor at aconcentration of 0.001 to 100 mM.

According to yet another preferred embodiment of the present invention,operation 1 may include (1-1) injecting a dispersion solution includinga dispersion solvent and nano-scale LED devices toward one surface ofthe base substrate on which the electrode line including the first andsecond electrodes spaced apart from each other is formed; and (1-2)manufacturing the nano-scale LED electrode assembly by applying thepower source to the electrode line to self-align the nano-scale LEDdevices. Here, the manufactured nano-scale LED electrode assembly may bethermally annealed at 600° C. to 1,000° C. for 0.5 to 10 minutes.

According to yet another preferred embodiment of the present invention,the first and second electrodes in operation 1 may be either spirally orinterdigitatedly disposed to be spaced apart from each other.

According to yet another preferred embodiment of the present invention,each of the nano-scale LED devices may include a first electrode layer;a first conductive semiconductor layer formed on the first electrodelayer; an active layer formed on the first conductive semiconductorlayer; a second conductive semiconductor layer formed on the activelayer; and a second electrode layer formed on the second conductivesemiconductor layer, and each of the nano-scale LED devices may furtherinclude an outer surface thereof coated with an insulating coating film.

According to yet another preferred embodiment of the present invention,the insulating coating film may be applied to cover the entire outersurface of the active layer.

According to yet another preferred embodiment of the present invention,outer surfaces of the first and second electrode layers of thenano-scale LED devices may not be coated with the insulating coatingfilm.

According to yet another preferred embodiment of the present invention,the plating time (T₁) in operation 2 may be in a range of 10 to 55minutes.

According to yet another preferred embodiment of the present invention,a width X of the first electrode, a width Y of the second electrode, adistance Z between the first electrode and the second electrode adjacentto the first electrode, and a height H of the nano-scale LED devices maysatisfy the following Relation 1:0.5Z≤H<X+Y+2Z  [Relation 1]

wherein 100 nm<X≤10 μm, 100 nm<Y≤10 μm, and 100 nm<Z≤10 μm.

According to yet another preferred embodiment of the present invention,each of the nano-scale LED devices may further include an insulatingbarrier formed on the base substrate in operation 1 to surround a regionof the electrode line in which the plurality of nano-scale LED devicesare positioned.

According to yet another preferred embodiment of the present invention,after operation 3, the manufactured nano-scale LED electrode assemblymay be thermally re-annealed at 600° C. to 1,000° C. for 0.5 to 10minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing in detail exemplary embodiments thereof with referenceto the accompanying drawings, in which:

FIGS. 1A through 1F are perspective view showing processes of a methodof manufacturing an electrode line according to one preferred embodimentof the present invention;

FIG. 2 is a perspective view of an electrode line including first andsecond electrodes formed on a base substrate according to one preferredembodiment of the present invention;

FIG. 3 is a plan view of the electrode line including the first andsecond electrodes formed on the base substrate according to onepreferred embodiment of the present invention;

FIG. 4 is a perspective view of an electrode line including first andsecond electrodes formed on a base substrate according to one preferredembodiment of the present invention;

FIG. 5 is a perspective view of a nano-scale LED device according to onepreferred embodiment of the present invention;

FIG. 6 is a vertical cross-sectional view of a conventional nano-scaleLED electrode assembly;

FIG. 7 shows a plan view and a vertical cross-sectional view of anano-scale LED device connected with the first and second electrodesaccording to one preferred embodiment of the present invention;

FIGS. 8A through 8F are perspective view showing manufacturing processesfor forming an insulating barrier on a base substrate according to onepreferred embodiment of the present invention;

FIGS. 9A through 9C are perspective view showing processes of a methodof manufacturing a nano-scale LED electrode assembly according to onepreferred embodiment of the present invention;

FIG. 10 is a diagram of an electroplating process performed to form ametal ohmic layer according to one preferred embodiment of the presentinvention;

FIG. 11 is a scanning electron microscope (SEM) image of a nano-scaleLED electrode assembly in which a metal ohmic layer is formed withoutperforming a rapid thermal annealing method according to one preferredembodiment of the present invention;

FIG. 12 is an SEM image of a nano-scale LED electrode assembly in whicha metal ohmic layer is formed after performing a rapid thermal annealingmethod according to one preferred embodiment of the present invention;

FIGS. 13 and 14 are diagrams showing a metal ohmic layer formed on onesurface of the electrode line on which the nano-scale LED devices areself-aligned according to one preferred embodiment of the presentinvention;

FIG. 15 is a blue electroluminescent image of a nano-scale LED devicefor a nano-scale LED electrode assembly according to Comparative Example1 of the present invention;

FIG. 16 is a blue electroluminescent image of a nano-scale LED devicefor a nano-scale LED electrode assembly according to Comparative Example2 of the present invention;

FIG. 17 is a blue electroluminescent image of a nano-scale LED devicefor a nano-scale LED electrode assembly according to Example 1 of thepresent invention;

FIG. 18 is a blue electroluminescent image of a nano-scale LED devicefor a nano-scale LED electrode assembly according to Example 2 of thepresent invention;

FIGS. 19 and 20 are graphs showing electroluminescence (EL) intensitiesmeasured while changing an alternating current (AC) voltage used todrive nano-scale LED electrode assemblies according to ComparativeExample 3 and Example 3, respectively; and

FIGS. 21 and 22 are images of the nano-scale LED electrode assemblies ofComparative Example 3 and Example 3 which emit light when an AC voltageis applied to the nano-scale LED electrode assemblies, respectively.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will be described indetail below with reference to the accompanying drawings. While thepresent invention is shown and described in connection with exemplaryembodiments thereof, it will be apparent to those skilled in the artthat various modifications can be made without departing from the scopeof the invention.

Unless specifically stated otherwise, all the technical and scientificterms used in this specification have the same meanings as what aregenerally understood by a person skilled in the related art to which thepresent invention belongs. In general, the nomenclatures used in thisspecification and the experimental methods described below are widelyknown and generally used in the related art.

In the description of the exemplary embodiments of the presentinvention, when it is assumed that individual layers, regions, patternsor structures are formed “on,” “over,” “above,” “under,” “beneath,” or“below” individual substrates, layers, regions, or patterns, it will beunderstood that the terms “on,” “over,” “above,” “under,” “beneath,” and“below” has meanings encompassing both “directly” and “indirectly.”

Also, in the description of the exemplary embodiments of the presentinvention, the terms “first electrode” and “second electrode” refer toelectrodes included in an electrode region in which nano-scale LEDs maybe substantially mounted, or an electrode region which may be furtherincluded in addition to the electrode region according to a method ofdisposing electrodes on a base substrate.

In addition, a nano-scale LED electrode assembly according to oneexemplary embodiment of the present invention refers to an electroderegion in which nano-scale LED devices may be substantially mounted, andnano-scale LED devices mounted in the electrode region.

Further, in the description of the exemplary embodiments of the presentinvention, the term “unit electrode” refers to an arrangement region inwhich two electrodes are disposed to arrange and independently drivenano-scale LED devices, and the term “area” of the unit electrode refersto an area of the arrangement region.

Hereinafter, the present invention will be described in further detailwith reference to the accompanying drawings.

As described above, as one of methods of manufacturing an LED electrodeassembly, in a method including separately and independently growing LEDdevices and then arranging the LED devices on electrodes, there is aneed to arrange the separate LED devices manufactured through a separateprocess on patterned electrode one by one. However, when theindependently grown LED devices are arranged on the electrodes to applya power source to the electrodes, contact resistance between the LEDdevices and the electrodes may occur, resulting in degraded lightemitting efficiency due to degraded light extraction efficiency.

Accordingly, the present invention seeks to solve the above problems byproviding a method of manufacturing a nano-scale LED electrode assemblyincluding a selective metal ohmic layer, which includes (1)manufacturing a nano-scale LED electrode assembly by self-aligningnano-scale LED devices on an electrode line including first and secondelectrodes which are formed on a base substrate to be spaced apart fromeach other; and (2) forming a metal ohmic layer on the nano-scale LEDelectrode assembly by immersing the nano-scale LED electrode assembly inan electroplating solution and applying a power source to one of thefirst and second electrodes of the nano-scale LED electrode assembly toperform an electroplating process for a plating time T₁ of 1 to 300minutes.

In this way, a conductive material may be deposited in a region in whichthe LED devices come in contact with the electrodes so as to enhanceconductivity between the LED devices and the electrodes and reduce aresistance value, thereby greatly improving light extraction efficiencyof the LED devices.

First, operation 1 includes manufacturing a nano-scale LED electrodeassembly by self-aligning nano-scale LED devices on an electrode lineincluding first and second electrodes which are formed on a basesubstrate to be spaced apart from each other. Preferably, operation 1may include 1-1) injecting a dispersion solution, which includes adispersion solvent and nano-scale LED devices, toward the electrode lineincluding the first and second electrodes formed on the base substrateto be spaced apart from each other, and 1-2) manufacturing thenano-scale LED electrode assembly in which the first and secondelectrodes are connected by applying a power source to the electrodeline to self-align the nano-scale LED devices.

First, a method of forming an electrode line on a base substrate will bedescribed. Specifically, FIGS. 1A through 1F are perspective viewshowing processes of a method of manufacturing an electrode line formedon a base substrate according to one preferred embodiment of the presentinvention. However, a process of manufacturing an electrode line fornano-scale LED devices is not limited to manufacturing processes as willbe described below.

First, as shown in FIG. 1A, one selected from the group consisting of aglass substrate, a crystal substrate, a sapphire substrate, a plasticsubstrate, and a flexible polymer film may be preferably used as thebase substrate 100 on which the electrode line is formed. Morepreferably, the base substrate 100 may be transparent. However, types ofthe base substrate 100 are not limited, and may be used withoutlimitation as long as the base substrate 100 is a general base substrateon which electrodes may be formed.

An area of the base substrate 100 is not limited, and may vary dependingon the area of the first electrode to be formed on the base substrate100, the area of the second electrode, the size of the nano-scale LEDdevices connected to the first and second electrodes, and the number ofthe nano-scale LED devices connected to the first and second electrodes.Preferably, the base substrate 100 may have a thickness of 100 μm to 1mm, but the present invention is not limited thereto.

Next, as shown in FIG. 1B, the base substrate 100 may be coated with aphotoresist (PR) to form a photoresist layer 101. The photoresist may bea photoresist generally used in the related art. A method of applyingthe photoresist onto the base substrate 100 to form the photoresistlayer 101 may include one selected from the group consisting of spincoating, spray coating, and screen printing, preferably spin coating,but the present invention is not limited thereto. Specific methods maybe performed using methods known in the related art. The photoresistlayer 101 may have a thickness of 0.1 to 10 μm. However, the thicknessof photoresist layer 101 may vary in consideration of the thickness ofelectrodes to be deposited onto the base substrate 100 later.

As such, after the photoresist layer 101 is formed on the base substrate100, a mask 102 having patterns 102 a and 102 b engraved therein tocorrespond to the electrode line (see FIG. 3) in which the first andsecond electrodes on the same plane are interdigitatedly disposed to bespaced apart from each other may be put on the photoresist layer 101, asshown in FIG. 1C, and a top surface of the mask 102 may be irradiatedwith ultraviolet rays.

Then, an operation of immersing the photoresist layer 101 in aconventional photoresist solvent to remove an exposed portion of thephotoresist layer 101 may be performed. In this way, the exposed portionof the photoresist layer on which the electrode line is to be formed asshown in FIG. 1D may be removed. The pattern 102 a corresponding to afirst electrode line belonging to the electrode line may have a width of100 nm to 50 μm, and the pattern 102 b corresponding to a secondelectrode line may have a width of 100 nm to 50 μm, but the presentinvention is not limited thereto.

Subsequently, as shown in FIG. 1E, an electrode-forming material 103 maybe deposited onto a region from which the photoresist layer is removedin the form of an electrode line mask. The electrode-forming material103 is a material used to form an electrode line including a firstelectrode and a second electrode formed to be spaced apart from thefirst electrode. In the case, the first electrode may be formed of oneor more metal materials selected from the group consisting of aluminum,titanium, indium, gold, and silver, or one or more transparent materialsselected from the group consisting of indium tin oxide (ITO), ZnO:Al,and a CNT-conductive polymer complex. When the electrode-formingmaterial includes two or more materials, the first electrode maypreferably have a structure in which the two or more materials arestacked. More preferably, the first electrode may be an electrode inwhich two materials such as titanium and gold are stacked. However, thefirst electrode is not limited to the description provided herein.

When the second electrode is formed of the electrode-forming material103, the second electrode may be formed of one or more metal materialsselected from the group consisting of aluminum, titanium, indium, gold,and silver, or one or more transparent materials selected from the groupconsisting of ITO, ZnO:Al, and a CNT-conductive polymer complex. Whenthe electrode-forming material 103 includes two or more materials, thesecond electrode may preferably have a structure in which the two ormore materials are stacked. More preferably, the second electrode may bean electrode in which two materials such as titanium and gold arestacked. However, the second electrode is not limited to the descriptionprovided herein.

The materials used to form the first electrode and the second electrodemay be the same or different.

The deposition of the electrode-forming material may be performed usingany one method such as a thermal deposition method, an e-beam depositionmethod, a sputtering deposition method, and a screen printing method,preferably a thermal deposition method, but the present invention is notlimited thereto.

After the electrode-forming material is deposited to form the electrodeline including a first electrode and a second electrode formed to bespaced apart from the first electrode, as shown in FIG. 1F, when thephotoresist layer applied onto the base substrate 100 is removed usingone photoresist stripper selected from acetone, 1-methyl-2-pyrrolidone(NMP), and dimethyl sulfoxide (DMSO), the electrode line 110 including afirst electrode 110 a deposited on the base substrate 100 and a secondelectrode 110 b formed to be spaced apart from the first electrode 110 amay be manufactured.

In the electrode line 110 of the present invention manufactured by theabove-described method, an area of a unit electrode, that is, an area ofan arrangement region in which two electrodes capable of arranging andindependently driving the nano-scale LED devices are disposed may bepreferably in a range of 1 μm² to 100 cm², more preferably in a range of10 μm² to 100 mm². However, the area of the unit electrode is notlimited to the above described areas. Also, the electrode line 110 mayone electrode or a plurality of unit electrodes.

In addition, the spacing between the first electrode 110 a and thesecond electrode 110 b in the electrode line 110 may be less than orequal to a height of the nano-scale LED devices. Therefore, thenano-scale LED devices are sandwiched between or connected across thefirst electrode 110 a and the second electrode 110 b in a state in whichthe nano-scale LED devices lie flat between the two electrodes.

Meanwhile, the electrode line 110 applicable to the present inventionmay be applied as long as a nano-scale LED can be mounted as the secondelectrode 110 b and the first electrode 110 a are on the same plane aswill be described below and formed to be spaced apart from the firstelectrode 110 a. In this case, a specific configuration of the firstelectrode 110 a and the second electrode 110 b spaced apart on the sameplane may vary according to purpose.

Next, FIG. 2 is a perspective view of an electrode line including firstand second electrodes formed on a base substrate according to onepreferred embodiment of the present invention. Here, first electrodes110 a and 110 a′ and/or second electrodes 110 b and 110 b′ may be formedon a base substrate 100. The term “on the base substrate” may mean astate in which at least one of the first electrodes 110 a and 110 a′ andsecond electrodes 110 b and 110 b′ may be directly formed on a surfaceof the base substrate 100 or may be formed to be spaced apart from a topsurface of the base substrate 100.

More specifically, as shown in FIG. 2, in a state in which all of thefirst electrodes 110 a and 110 a′ and the second electrodes 110 b and110 b′ are directly formed on a surface of the base substrate 100, thefirst electrode 110 a′ and the second electrode 110 b′ may beinterdigitatedly disposed to be spaced apart from each other and thefirst electrode 110 a′ and the second electrode 110 b′ are on the sameplane.

FIG. 3 is a plan view of the electrode line including the first andsecond electrodes formed on the base substrate according to onepreferred embodiment of the present invention. Here, in a state in whichall of first electrodes 110 a and 110 c and second electrodes 110 b and110 d are directly formed on a surface of the base substrate 100, thefirst electrode 110 c and the second electrode 110 d may be spirallydisposed spaced apart on the same plane.

As such, when the electrode lines are configured to be interdigitatedlyor spirally disposed, the nano-scale LED devices included on the basesubstrate 100 having a limited area may be arranged once to increase adrive area of a unit electrode that is independently operable, therebyincreasing the number of nano-scale LED devices mounted on the unitelectrode. Thus, since the intensity of light emitted from the LEDs perunit area increases, the LEDs may utilized in various photoelectricdevices that require higher brightness per unit area.

Meanwhile, FIGS. 2 and 3 are preferred embodiments, but the presentinvention is not limited thereto. For example, two electrodes may berealized by being widely modified to have all possible structures inwhich the two electrodes are spaced at a predetermined distance fromeach other.

Also, unlike the electrode line according to one preferred embodiment ofthe present invention as shown in FIG. 2, according to anotherembodiment of the present invention, the second electrode may be formedto be spaced apart from an upper portion of the base substrate.

Specifically, FIG. 4 is a perspective view of an electrode lineincluding first and second electrodes formed on a base substrateaccording to one preferred embodiment of the present invention. Here,first electrodes 210 a and 210 a′ may be directly formed on a surface ofa base substrate 200, or second electrodes 210 b and 210 b′ may beformed to be spaced apart from an upper portion of the base substrate200. In this case, the first electrode 210 a′ and the second electrode210 b′ may be interdigitatedly disposed to be spaced apart on the sameplane.

Hereinafter, a configuration in which first and second electrodes areinterdigitatedly disposed on the same plane will be mainly described.However, the first and second electrodes may be directly formed on asurface of a base substrate, or may be formed to be spaced apart from asurface of the base substrate. In this case, the first and secondelectrodes may not be on the same plane.

Next, a dispersion solution including a plurality of nano-scale LEDdevices, which is injected toward an electrode line, will be described.The dispersion solution may be prepared by mixing a plurality ofnano-scale LED devices and a dispersion solvent. The dispersion solventmay be in an ink or paste phase. Preferably, the dispersion solvent mayinclude one or more selected from the group consisting of acetone,water, alcohol, and toluene, more preferably acetone. However, types ofthe dispersion solvent are not limited to the above described solvents,and may be used without limitation as long as they are solvents that maybe easily volatilized without exerting physical and chemical effects onthe nano-scale LED devices.

Preferably, the nano-scale LED devices may be included at a content of0.001 to 100 parts by weight, based on 100 parts by weight of thedispersion solvent. When the nano-scale LED devices are included at acontent of less than 0.001 parts by weight, the number of the nano-scaleLED devices connected to the electrodes may be reduced, which makes itdifficult to exert normal functions of the nano-scale LED electrodeassembly. To solve the problems, the dispersion solution may be addeddropwise several times. When the content of the nano-scale LED devicesis greater than 100 parts by weight, an arrangement between theplurality of nano-scale LED devices may be disturbed.

The nano-scale LED devices may be used without limitation as long asthey are nano-scale LED devices generally used for lightings ordisplays. Preferably, the nano-scale LED devices may have a height of100 nm to 10 μm, more preferably a height of 500 nm to 5 μm. When theheight of the nano-scale LED devices is less than 100 nm, it isdifficult to manufacture high-efficiency LED devices. On the other hand,when the height of the nano-scale LED devices is greater than 10 μm,light emitting efficiency of the LED devices may be degraded. Thenano-scale LED devices may have various shapes such as a cylindricalshape, a rectangular parallelepiped shape, etc., preferably acylindrical shape, but the shape of the nano-scale LED devices is notlimited to the above described shapes.

Meanwhile, the nano-scale LED devices according to preferred embodimentsof the present invention are disclosed in Korean Patent Application No.2011-0040174 filed by the present inventors, the disclosure of which isincorporated herein by reference in its entirety.

Hereinafter, in the description of the nano-scale LED devices, the terms“above,” “below,” “on,” “under,” “upper”, and “lower” refer to verticalupper and lower directions with respect to each of layers included inthe nano-scale LED devices.

Each of the nano-scale LED devices may include a first electrode layer,a first conductive semiconductor layer formed on the first electrodelayer, an active layer formed on the first conductive semiconductorlayer, a second conductive semiconductor layer formed on the activelayer, and a second electrode layer formed on the second conductivesemiconductor layer.

Specifically, FIG. 5 is a perspective view showing one exemplaryembodiment of a nano-scale LED device included in the present invention.Here, a nano-scale LED device 20 includes a first electrode layer 21, afirst conductive semiconductor layer 22 formed on the first electrodelayer 21, an active layer 23 formed on the first conductivesemiconductor layer 22, a second conductive semiconductor layer 24formed on the active layer 23, and a second electrode layer 25 formed onthe second conductive semiconductor layer 24.

First, the first electrode layer 21 will be described.

The first electrode layer 21 may be formed of a metal or a metal oxideused for electrodes of conventional LED devices. Preferably, chromium(Cr), titanium (Ti), aluminum (Al), gold (Au), nickel (Ni), ITO, and anoxide or alloy thereof may be used alone or in combination thereof, butthe present invention is not limited thereto. Preferably, the firstelectrode layer 21 may have a thickness of 1 to 100 nm, but the presentinvention is not limited thereto.

Next, the first conductive semiconductor layer 22 formed on the firstelectrode layer 21 will be described. The first conductive semiconductorlayer 22 may, for example, include an n-type semiconductor layer. Whenthe nano-scale LED device 20 is a blue light emitting device, the n-typesemiconductor layer may be formed of a semiconductor material having acompositional formula of In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1,0≤x+y≤1), for example, one or more selected from the group consisting ofInAlGaN, GaN, AlGaN, InGaN, AlN, InN, etc. Also, the first conductivesemiconductor layer may be doped with a first conductive dopant (e.g.,Si, Ge, Sn, etc.). Preferably, the first conductive semiconductor layer22 may have a thickness of 500 nm to 5 μm, but the present invention isnot limited thereto. The color of light emitted from the nano-scale LEDdevice 20 is not limited to a blue color. When the colors of the emittedlight are different, different types of Group III-V semiconductormaterials may be used for the n-type semiconductor layer withoutlimitation.

Next, the active layer 23 formed on the first conductive semiconductorlayer 22 will be described. When the nano-scale LED device 20 is a bluelight emitting device, the active layer 23 may be disposed on the firstconductive semiconductor layer 22, and may be formed in a single quantumwell (SQW) or multiple quantum well (MQW) structure. A cladding layer(not shown) doped with a conductive dopant may be formed on and/or underthe active layer 23. In this case, the cladding layer doped with theconductive dopant may be realized as an AlGaN layer or an InAlGaN layer.In addition, materials such as AlGaN, AlInGaN, and the like may be usedfor the active layer 23. When an electric field is applied to the activelayer 23, light may be generated due to coupling of electron-hole pairs.Preferably, the active layer 23 may have a thickness of 10 nm to 200 nm,but the present invention is not limited thereto. The active layer 23may be disposed at various positions according to the types of thenano-scale LED device 20.

The light color of the nano-scale LED is not limited to the blue color.When the light color is different, different types of Group III-Vsemiconductor materials may be used for the active layer. The color oflight emitted from the nano-scale LED device 20 is not limited to a bluecolor. When the colors of the emitted light are different, differenttypes of Group III-V semiconductor materials may be used for the activelayer 23 without limitation.

Next, the second conductive semiconductor layer 24 formed on the activelayer 23 will be described. When the nano-scale LED device 20 is a bluelight emitting device, the second conductive semiconductor layer 24 maybe formed on the active layer 23. In this case, the second conductivesemiconductor layer 24 may be realized as at least one p-typesemiconductor layer. Here, the p-type semiconductor layer may be formedof a semiconductor material having a compositional formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1), for example, one ormore selected from the group consisting of InAlGaN, GaN, AlGaN, InGaN,AlN, InN, etc. Also, the second conductive semiconductor layer 24 may bedoped with a second conductive type dopant (e.g., Mg). Here, a lightemitting structure may include the first conductive semiconductor layer22, the active layer 23, and the second conductive semiconductor layer24 as minimum components. Also, the light emitting structure may furtherinclude a phosphor layer, an active layer, a semiconductor layer, and/oran electrode layer formed on/under each layer. Preferably, the secondconductive semiconductor layer 24 may have a thickness of 50 nm to 500nm, but the present invention is not limited thereto. The color of lightemitted from the nano-scale LED device 20 is not limited to a bluecolor. When the colors of the emitted light are different, differenttypes of Group III-V semiconductor materials may be used for the p-typesemiconductor layer without limitation.

Then, the second electrode layer 25 formed on the second conductivesemiconductor layer 24 will be described.

The second electrode layer 25 may be formed of a metal or a metal oxideused for electrodes of conventional LED devices. Preferably, chromium(Cr), titanium (Ti), aluminum (Al), gold (Au), nickel (Ni), ITO, and anoxide or alloy thereof may be used alone or in combination thereof, butthe present invention is not limited thereto. Preferably, the secondelectrode layer 25 may have a thickness of 1 to 100 nm, but the presentinvention is not limited thereto.

Meanwhile, the nano-scale LED device 20 included in the nano-scale LEDelectrode assembly according to the present invention may furtherinclude an insulating coating film 26 with which an outer surface of thenano-scale LED device 20 is coated.

Specifically, referring to FIG. 5, the insulating coating film 26 may beapplied to cover the entire outer surface of the active layer 23.Preferably, the insulating coating film 26 may be applied onto an outersurface of one of the first conductive semiconductor layer 22 and thesecond conductive semiconductor layer 24 to prevent the durability ofthe nano-scale LED device from being deteriorated due to damage to theouter surface of the semiconductor layer.

The insulating coating film 26 may prevent an electrical short circuitfrom occurring when the active layer of the nano-scale LED device 20comes in contact with the electrode line included in the nano-scale LEDelectrode assembly. Also, the insulating coating film 26 may protect theentire outer surface of the active layer 23 of the nano-scale LED device20 to prevent surface defects of the active layer 23, thereby preventinglight emitting efficiency from being deteriorated.

When the separate nano-scale LED devices are disposed one by one betweentwo different electrodes to be connected with each other, an electricalshort circuit occurring due to the contact between the active layer andthe electrodes may be prevented. However, it is difficult to physicallymount the nano-scale LED devices having a nano-scale size one by one onthe electrodes. Therefore, in the present invention, the electrodes maybe mounted by applying a first power source to the electrode line inoperation 2, as will be described below, to self-align the nano-scaleLED devices between the two different electrodes. In this case, thenano-scale LED devices may be changed in position through movement andalignment between the two different electrodes. In this process, anelectrical short circuit may be frequently caused since the active layerof the nano-scale LED device may come in contact with the electrodeline.

Meanwhile, when the nano-scale LED device is stood upright on theelectrode, an electrical short-circuit problem occurring due to thecontact between the active layer and the electrode line may beprevented. That is, when the nano-scale LED device is not stood uprighton the electrode but is laid flat on the electrode, the active layer maycome in contact with the electrode line. In this case, the nano-scaleLED device may not be connected to the two different electrodes, but noelectrical short-circuit problem may occur.

Specifically, FIG. 6 is a vertical cross-sectional view of aconventional nano-scale electrode assembly. Here, it can be seen that afirst semiconductor layer 71 a of a first nano-scale LED device 71 isconnected to a first electrode line 61, a second semiconductor layer 71c is connected to a second electrode line 62, and the first nano-scaleLED device 71 is stood upright to be connected to two electrodes 61 and62 positioned in a vertical direction. When the nano-scale LED device 71is connected to the two electrodes in the electrode assembly as shown inFIG. 6, an active layer 71 b of the device is not be likely to come incontact with one of the two different electrodes 61 and 62, therebypreventing an electrical short circuit from occurring due to the contactbetween the active layer 71 b and the two electrodes 61 and 62.

On the other hand, a second nano-scale LED device 72 may be laid flat onthe first electrode 61 as shown in FIG. 6. In this case, an active layer72 b of the second nano-scale LED device 72 may come in contact with thefirst electrode 61. Here, problems in the connection between the secondnano-scale LED device and the first and second electrodes 61 and 62rather than the electrical short circuit may occur. Therefore, whenouter circumferential surfaces of the first semiconductor layer 71 a,the active layer 71 b and the second semiconductor layer 71 c of thefirst nano-scale LED device are coated with an insulating coating film,the insulating coating film may have only a purpose and effect ofreducing light emitting efficiency by preventing the outer surface ofthe nano-scale LED device from being damaged.

However, unlike the conventional nano-scale electrode assembly as shownin FIG. 6, according to the present invention, the two differentelectrodes may be disposed to be spaced apart on the same plane (seeFIG. 2). Also, since the nano-scale LED device is laid flat to beconnected with the two electrodes in a state in which the nano-scale LEDdevice is parallel to the same plane on which the two electrodes areformed, an electrical short-circuit problem which does not occur in theconventional nano-scale electrode assembly when the active layer of thenano-scale LED device comes in contact with the electrodes mayinevitably occur. Therefore, to prevent the electrical short-circuitproblem, it is desirable to provide an insulating coating film which isapplied to cover the entire outer surface of the active layer of thenano-scale LED device.

In addition, like the nano-scale LED device included in the nano-scaleLED electrode assembly according to the present invention, the activelayer may be inevitably exposed to the outside in the nano-scale LEDdevice having a structure in which the first semiconductor layer, theactive layer, the second semiconductor layer are sequentially arrangedin a vertical direction. Also, in the LED device having such astructure, the active layer may not only be disposed at the center ofthe device in a longitudinal direction, but also may be biased toward acertain semiconductor layer, thereby increasing the possibility ofcontact between the electrode and the active layer. Therefore, aninsulating coating film which is applied to cover the entire outersurface of the active layer may be preferably provided to achieve thepurpose of the present invention. As a result, the insulation film maybe necessary.

Specifically, FIG. 7 shows a plan view and a vertical cross-sectionalview of a nano-scale LED device connected to the first and secondelectrodes according to one preferred embodiment of the presentinvention. Specifically, as shown in a cross section taken along lineA-A in FIG. 7, an active layer 121 b of nano-scale LED devices 121 isnot disposed at a central portion of the nano-scale LED device 121, butmay be disposed to be biased toward a left side thereof. In this case, aportion of the active layer 121 b may be very likely to be connected toan electrode 111, causing an electrical short circuit, which may causedefects in the nano-scale LED electrode assembly. To solve the aboveproblems, the nano-scale LED device provided in the present inventionmay be coated with an insulating coating film to cover the entire outersurface of the active layer. As a result, even when the active layer 121b is disposed across the electrode, like the first nano-scale LED device121 shown in FIG. 7, an electrical short circuit may be prevented due tothe insulating coating film.

As described above, referring to FIG. 6, the insulating coating film 26may preferably include one or more selected from the group consisting ofsilicon nitride (Si₃N₄), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃),hafnium oxide (HfO₂), yttrium oxide (Y₂O₃), and titanium dioxide (TiO₂).More preferably, the insulating coating film 26 may be formed of theabove described substances, or may be transparent, but the presentinvention is not limited thereto. When the insulating coating film 26 istransparent, the insulating coating film 26 may play its original role,and simultaneously minimize a reduction in light emitting efficiencythat may rarely occur through coating with the insulating coating film26.

Meanwhile, according to one preferred embodiment of the presentinvention, an outer surface of one of the first electrode layer 21 andthe second electrode layer 25 of the nano-scale LED device may not becoated with the insulating coating film 26. More preferably, both thetwo electrode layers 11 and 12 may not be coated with the insulatingcoating film 26.

In this case, the two electrode layers 21 and 25 have to be electricallyconnected to other electrodes. However, when the two electrode layers 21and 25 are coated with the insulating coating film 26, the electricalconnection may be disturbed. As a result, light emitted from thenano-scale LED device may be reduced, or no light may be emitted fromthe nano-scale LED device since the nano-scale LED device is notelectrically connected to the electrode. However, since there are noproblems when two electrode layers 21 and 25 are electrically connectedto the different electrodes, the insulating coating film 26 may beincluded in the remaining region of the electrode layers after excludingthe end portions of the two electrode layers 21 and 25.

Also, according to one preferred embodiment of the present invention,the nano-scale LED device 20 may further include a hydrophobic film 27formed on the insulating coating film 26. The hydrophobic film 27 maygive a hydrophobic property to a surface of the nano-scale LED device 20so as to prevent aggregation between the LED devices. When thenano-scale LED devices 20 are mixed with a dispersion solvent, theaggregation between the nano-scale LED devices may be minimized toprevent characteristics of the separate nano-scale LED devices frombeing degraded. Also, when a power source is applied to the electrodeline, the nano-scale LED devices 20 may be more easily aligned inpredetermined positions.

The hydrophobic film 27 may be formed on the insulating coating film 26.In this case, types of the hydrophobic film 27 that may be used hereinmay be used without limitation as long as they can be formed on theinsulating coating film 26 to prevent the nano-scale LED devices frombeing aggregated. Preferably, the hydrophobic film 27 may be formed ofat least one selected from the group consisting of self-assembledmonolayers (SAMs) such as octadecyltrichlorosilane, (OTS),fluoroalkyltrichlorosilane, and perfluoroalkyltriethoxy-silane, andfluoropolymers such as Teflon and Cytop, which may be used alone or in acombination thereto, but the present invention is not limited thereto.

Meanwhile, the height of the nano-scale LED device included in thenano-scale LED electrode assembly according to the present invention maysatisfy the following Relation 1 to realize an electrical connectionbetween the nano-scale LED device and the two different electrodes. Whenthe nano-scale LED device is not electrically connected to the twoelectrodes, the nano-scale LED device having no electrical connectionwith the two electrodes does not emit light even when a power source isapplied to the electrode line, which makes it impossible to achieve theobjects of the present invention.

Relation 1 is expressed as follows:0.5Z≤H<X+Y+2Z  [Relation 1]

Preferably, Relation 1 may satisfy Z≤H<X+Y+2Z, more preferably Z≤H≤X+Y+Z(wherein 100 nm<X≤10 μm, 100 nm<Y≤10 μm, and 100 nm<Z≤10 μm). The symbol‘X’ represents a width of the first electrode included in the electrodeline, the symbol ‘Y’ represents a width of the second electrode, thesymbol ‘Z’ represents a distance between a first electrode and a secondelectrode adjacent to the first electrode, and the symbol ‘H’ representsa height of the nano-scale LED device. Here, when the first and secondelectrodes are provided in a plural number, the distance Z between thetwo electrodes may be the same or different.

A portion of the nano-scale LED device which is electrically connectedwith the two different electrodes may be at least one layer (or one ofthe second conductive semiconductor layer and the second electrodelayer) of the first electrode layer and the first conductivesemiconductor layer of the nano-scale LED device.

When the height of the nano-scale LED device is significantly smallerthan the distance between the two different electrodes, it may bedifficult for the nano-scale LED device to be connected with both of thetwo electrodes. Therefore, the nano-scale LED device may be a nano-scaleLED device having a height satisfying a requirement of 0.5Z≤H inRelation 1. When the height of the nano-scale LED device does notsatisfy the requirement of 0.5Z≤H in Relation 1, the nano-scale LEDdevice may not be electrically connected with the first and secondelectrodes, but may be electrically connected with only one of the firstand second electrodes. More preferably, as shown in FIG. 7, since asecond nano-scale LED device 122 may be sandwiched between the firstelectrode 111 and the second electrode 132 to be electrically connectedtherewith, the nano-scale LED device provided in the present inventionmay be an LED device that satisfies a requirement of Z≤H in Relation 1.

Meanwhile, when the height H of the nano-scale LED device is increasedin consideration of the width X of the first electrode, the width Y ofthe second electrode, and the electrode distance Z between the first andsecond electrodes, a portion of a nano-scale LED device 123 of FIG. 7(excluding both ends thereof) may be independently connected to a firstelectrode 112 and a second electrode 132. When the active layer of thenano-scale LED device 123 is connected as described above, an electricalshort circuit between the electrode and the nano-scale LED device 123may be caused when the nano-scale LED device is not coated with theinsulating coating film. However, in the nano-scale LED device accordingto the present invention, since the insulating coating film is coated tocover the entire outer surface of the active layer. Thus, like thenano-scale LED device 123 as shown in FIG. 7, even when the portion ofthe nano-scale LED device excluding both ends thereof is connected withthe electrodes, the nano-scale LED device may be electrically connectedto the electrodes without causing an electrical short circuit.

However, since the height H of the nano-scale LED device is increased inconsideration of the width X of the first electrode, the width Y of thesecond electrode, and the electrode distance Z between the first andsecond electrodes, the nano-scale LED device that is not electricallyconnected to the electrodes may be included in the nano-scale LEDelectrode assembly when the height H of the nano-scale LED device doesnot satisfy a requirement of H<X+Y+2Z. Specifically, a nano-scale LEDdevice 124 may be electrically connected to one first electrode 112 andtwo second electrodes 132 and 133 at the same time, as shown in FIG. 7.Here, the height of the nano-scale LED device satisfying such a case maynot satisfy a requirement of H<X+Y+2Z in Relation 1. In this case, sincethe active layer is coated with the insulating coating film in thenano-scale LED device according to the present invention, a problemregarding an electrical short circuit caused due to the contact of thenano-scale LED device with the first electrode 112 may be solved, butthe nano-scale LED device is not substantially electrically connected asboth ends of the nano-scale LED device 124 are connected with the twosecond electrodes 132 and 133. As a result, such a nano-scale LED device124 may have a problem in that no light is emitted even when a powersource is applied to the electrode line. Therefore, the height H of thenano-scale LED device should satisfy the requirement of H<X+Y+2Z inRelation 1. However, when the active layer of the nano-scale LED deviceis biased toward a certain conductive semiconductor layer 125 b (seeFIG. 7), and a portion of the nano-scale LED device connected with theelectrode is not the electrode layer and/or the conductive semiconductorlayer but the active layer coated with the insulating coating film, anelectrical short circuit does not occur due to insulating coating film,but the nano-scale LED device may not be electrically connected with theelectrode line. Specifically, as shown in FIG. 7, a nano-scale LEDdevice 125 may be connected to the first electrode 111 and the secondelectrode 131 at the same time. However, referring to the cross sectiontaken along line B-B in FIG. 7, it is seen that a portion of thenano-scale LED device connected with the first electrode 111 is aportion of an active layer 125 c coated with the insulating coatingfilm, and a first electrode layer 125 a and the first conductivesemiconductor layer 125 b are not connected to the first electrode 111.In this case, since a portion of the active layer 125 c in thenano-scale LED device is coated with the insulating coating film, anelectrical short circuit does not occur, but the first electrode layer125 a and the first conductive semiconductor layer 125 b may not beconnected to the first electrode 111. Therefore, the nano-scale LEDdevice 125 may not emit light when a power source is applied to theelectrode line. In cases that may happen in such circumstances, as theheight H of the nano-scale LED device may satisfy a requirement ofX+Y+Z<H<X+Y+2Z in Relation 1, the height H of the nano-scale LED devicemay more preferably satisfy a requirement of X+Y+Z in Relation 1. Inthis case, the nano-scale LED device has an advantage in that thenano-scale LED electrode assembly electrically connected without causingan electrical short circuit regardless of the position of the activelayer coated with the insulating coating film in a longitudinaldirection may be realized.

Meanwhile, the nano-scale LED device may further include an insulatingbarrier formed on the base substrate in operation 1 to surround a regionof the electrode line on which a plurality of nano-scale LED devices aredisposed. When the insulating barrier is formed on the base substrate, adispersion solution including the plurality of nano-scale LED devicesmay be provided in the region of the electrode line surrounded by theinsulating barrier. The insulating barrier may serve to dispose thenano-scale LED devices in a desired region of the electrode line bypreventing the dispersion solution including the nano-scale LED devicesfrom spreading to a region other than the region of the electrode linein which the nano-scale LED devices are to be provided when thedispersion solution including the nano-scale LED devices is applied tothe electrode line.

The insulating barrier may be manufactured by a manufacturing process aswill be described below, but a method of manufacturing the insulatingbarrier is not limited thereto.

Specifically, FIGS. 8A through 8F are schematic diagram showingmanufacturing processes for forming an insulating barrier on a basesubstrate and an electrode line formed on the base substrate accordingto one preferred embodiment of the present invention. As describedabove, after the electrode line deposited onto the base substrate ismanufactured, the insulating barrier may be manufactured.

First, as shown in FIG. 8A, a base substrate 100 having an electrodeline 110 formed on one surface thereof is manufactured. Here, theelectrode line 110 includes a first electrode 110 a, and a secondelectrode 110 b formed to be spaced apart from the first electrode 110a. Next, as shown in FIG. 8B, an insulation layer 104 may be formed onthe base substrate 100 and the electrode line 110 including the firstand second electrodes 110 a and 110 b formed on the base substrate 100.The insulation layer 104 may be a layer for forming the insulatingbarrier after undergoing a process as will be described below. In thiscase, the insulation layer 104 may be formed of an insulating materialgenerally used in the related art, preferably, one or more selected fromthe group consisting of inorganic insulating materials such as silicondioxide (SiO₂), silicon nitride (Si₃N₄), aluminum oxide (Al₂O₃), hafniumoxide (HfO₂), yttrium oxide (Y₂O₃) and titanium dioxide (TiO₂), andvarious transparent polymeric insulating materials. When the basesubstrate 100 and the electrode lines 103 a and 103 b formed on the basesubstrate 100 are coated with an inorganic insulation layer, theinsulation layer 104 may be formed using a method selected from thegroup consisting of a chemical vapor deposition method, an atomic layerdeposition method, an e-beam deposition method, and a spin coatingmethod, preferably a chemical vapor deposition method, but the presentinvention is not limited thereto. Also, a method for applying thepolymeric insulation layer may be performed using a method selected fromthe group consisting of spin coating, spray coating, and screenprinting, preferably a spin coating method, but the present invention isnot limited thereto. A specific coating method may be performed withmethods known in the related art. The coated insulation layer 104 mayhave a thickness such that the nano-scale LED device does not spreadover the region of the electrode line in which the nano-scale LED deviceis to be provided and the thickness of the insulation layer 104 does nothave an effect on subsequent processes. Thus, the thickness of theinsulation layer 104 may be preferably in a range of 0.1 to 100 μm, morepreferably in a range of 0.3 to 10 μm.

Next, a photoresist layer 105 may be formed by coating the insulationlayer 104 with a photoresist (PR). The photoresist may be a photoresistwidely used in the related art. A method for coating the insulationlayer 104 with the photoresist may include one method selected from thegroup consisting of spin coating, spray coating, and screen printing,preferably spin coating, but the present invention is not limitedthereto. Specific coating methods may be performed with methods known inthe related art. Preferably, the thickness of the photoresist layer 105to be applied is larger than the thickness of the insulation layer 104applied through a mask used for an etching process. Therefore, thephotoresist layer 105 may have a thickness of 1 μm to 20 μm. However,the thickness of the photoresist layer 105 to be applied may vary inconsideration of a purpose thereof.

Subsequently, as shown in FIG. 8C, after the photoresist layer 105 isformed on the insulation layer 104, a mask 106 having a shapecorresponding to a horizontal cross section of the insulating barriermay be put on the photoresist layer 105, and a top surface of the mask106 may be exposed to UV rays.

Thereafter, an operation of immersing the exposed photoresist layer in aconventional photoresist solvent for removal thereof may be performed.In this way, as shown in FIG. 8D, a portion of the exposed photoresistlayer corresponding to the region of the electrode line on which thenano-scale LED device is mounted may be removed.

Then, an operation of removing a portion of the exposed insulation layerby etching a portion of the insulation layer exposed through removal ofthe photoresist layer may be performed. The etching may be performedthrough wet etching or dry etching, preferably dry etching. A specificmethod for performing the etching process may be performed with methodsknown in the related art. The dry etching may be performed using one ormore methods selected from the group consisting of plasma etching,sputter etching, reactive ion etching, and reactive ion beam etching.However, the specific etching method is not limited to theabove-described methods. When the exposed insulation layer is removedthrough the etching, the base substrate 100 and electrode lines 110 a′and 110 b′ may be exposed, as shown in FIG. 8E.

Next, as shown in FIG. 8F, when the photoresist 105 (see FIG. 8E)applied on the base substrate 100 is removed using one photoresiststripper selected from the group consisting of 1-methyl-2-pyrrolidone(NMP) and dimethyl sulfoxide (DMSO), an insulating barrier 104 may beformed on a region other than a region P (see FIG. 8E) on which thenano-scale LED device is substantially mounted on the base substrate100.

In this way, when the insulating barrier 104 is formed on the basesubstrate 100, a dispersion solution including the plurality ofnano-scale LED devices may be injected toward the region of theelectrode line surrounded by the insulating barrier 104.

Specifically, FIGS. 9A through 9C are perspective view showing processesof a method of manufacturing a nano-scale LED electrode assemblyaccording to one preferred embodiment of the present invention. As shownin FIG. 9A, a dispersion solution 30 including a plurality of nano-scaleLED devices 20 may be injected toward a region of electrode lines 110 aand 110 b surrounded by the insulating barrier 104 formed on the basesubstrate 100. In this case, the dispersion solution 30 including thenano-scale LED devices 20 may be directly disposed in a desired regionof the electrode line, compared to when the insulating barrier 104 isnot formed on the base substrate 100. Also, after the dispersionsolution 30 is injected, the nano-scale LED devices 20 in the dispersionsolution 30 spread to the edges of the electrode line to prevent thenano-scale LED devices 20 from being disposed in a region of theelectrode line on which the nano-scale LED devices 20 are not mountedand/or an electrode line-free region. After the dispersion solution 30including the plurality of nano-scale LED devices 20 is injected, when apower source is applied to the electrode lines 110 a and 110 b as shownin FIG. 9B, the plurality of nano-scale LED devices 20 are self-alignedon the electrode lines 110 a and 110 b, as shown in FIG. 9C.

Next, the nano-scale LED electrode assembly to which the first electrodeand the second electrode are connected is manufactured by applying apower source to the electrode line to self-align the nano-scale LEDdevices.

In general, since the LED devices have a size sufficient for direct andphysical arrangement, the LED devices may be connected to both of thedifferent electrodes formed spaced apart on the same plane. However,since the size of the nano-scale LED devices of the present invention istoo small for direct and physical arrangement, it is difficult toconnect the different nano-scale electrodes spaced apart on the sameplane with each other. Also, since the nano-scale LED devices of thepresent invention may have a cylindrical shape, the nano-scale LEDdevices may move by rolling due to such a shape. As a result, even whenthe first electrode and the second electrode are disposed to beconnected to each other, the relative positions of the first electrodeand the second electrode may be easily changed.

To solve the above problems, in the present invention, since a firstpower source is applied to the electrode line to self-align thenano-scale LED devices, the first electrode and the second electrode maybe connected, that is, electrically connected to each other.

The power source applied to the electrode line may be a variable powersource having a predetermined amplitude and period, and may have pulsewaves composed of waveforms such as sinusoidal waves, for example, sinewaves, and waveforms other than the sinusoidal wave. For example, an ACpower source may be applied to the first electrode, or a direct current(DC) power source may be repeatedly applied to the first electrode 1,000times per second at a voltage of 0 V, 30 V, 0 V, 30 V, 0 V, and 30 V.Conversely, the DC power source may be repeatedly applied to the secondelectrode at a voltage of 30 V, 0 V, 30 V, 0 V, 30 V, and 0 V togenerate a variable power source having a predetermined amplitude andperiod.

Preferably, the power source may have a voltage (amplitude) of 0.1 V to1,000 V and a frequency of 10 Hz to 100 GHz. The self-aligned nano-scaleLED devices may be included in a solvent, and then injected toward theelectrode line. In this case, the solvent may be evaporated whiledropping onto the electrodes. Also, since charges are asymmetricallyinduced to the nano-scale LED devices due to induction of an electricfield generated by a potential difference between the two electrodes,both ends of the nano-scale LED devices may be self-aligned between thetwo facing different electrodes. Preferably, the nano-scale LED devicesmay be connected to the two different electrodes by applying a powersource for 5 to 120 seconds.

Meanwhile, the number N of the nano-scale LED devices connected to thefirst electrode and the second electrode may depend on several variablesthat are adjustable herein. The variables may include a voltage V of theapplied power source, a frequency F (Hz) of the power source, aconcentration C (% by weight of the nano-scale LEDs) of the dispersionsolution including the nano-scale LED devices, a distance Z between thetwo electrodes, and an aspect ratio AR of the nano-scale LEDs (whereinAR=H/D, and D represents a diameter of the nano-scale LED). As a result,the number N of the nano-scale LED devices connected to the firstelectrode and the second electrode may be proportional to the voltage V,the frequency F (Hz), the concentration C of the dispersion solutionincluding the nano-scale LED devices, and the aspect ratio AR of thenano-scale LEDs, and inversely proportional to the distance Z betweenthe two electrodes.

Thus, the nano-scale LED devices may be self-aligned between the twodifferent electrodes by induction of the electric field generated due toa potential difference between the two electrodes. Therefore, as theintensity of the electric field increases, the number of the nano-scaleLED devices connected with the two electrodes may increase. Also, theintensity of the electric field may be proportional to the potentialdifference V between the two electrodes, and be inversely proportionalto the distance Z between the two electrodes.

Next, as the concentration C (% by weight of the nano-scale LED devices)of the dispersion solution including the nano-scale LED devicesincreases, the number of the LED devices connected to the two electrodesmay increase.

Subsequently, in case of the frequency H (Hz) of the power source, sincea difference in charges generated in the nano-scale LED devices variesaccording to the frequency, the number of the nano-scale LED devicesconnected to the two electrodes may increase with an increasedfrequency. However, since charges may not be induced when the frequencyis greater than a predetermined value, the number of the nano-scale LEDdevices connected to the two electrodes may decrease.

Finally, when the aspect ratio of the nano-scale LED device increases,the charges induced by the electric field increase. Therefore, a largernumber of the nano-scale LED devices may be aligned. Also, inconsidering the electrode line has a limited area in a spatial aspectfor alignment of the nano-scale LED devices, in a state in which thenano-scale LED devices have a fixed height, the diameter of thenano-scale LED devices may decrease. Therefore, when the aspect ratioincreases, the number of the nano-scale LED devices to be connected tothe two electrode lines having a limited area may increase.

In the present invention, a variety of the above-described factors maybe controlled to adjust the number of the LED devices connected to thetwo electrodes according to purpose.

Preferably, the number of the nano-scale LED devices per area (100×100μm²) of the electrode line on which the nano-scale LED devices may besubstantially mounted may be in a range of 2 to 100,000, more preferablyin a range of 10 to 10,000. Since the plurality of nano-scale LEDdevices are included in one nano-scale LED electrode assembly of thepresent invention, functional degradation or loss of the nano-scale LEDelectrode assembly may be minimized due to the malfunction of some ofthe plurality of nano-scale LED devices. Also, when the number of thenano-scale LED devices is greater than 100,000, manufacturing costs mayincrease, and it may be difficult to align the nano-scale LED devices.

Next, in the nano-scale LED electrode assembly manufactured byself-aligning the nano-scale LED devices in operation 1, the dispersionsolvent included in the dispersion solution may be removed using a rapidthermal annealing (RTA) method. Rapid thermal annealing is a method ofthermally annealing a dispersion solution at a high temperature for ashort period of time. Thus, the dispersion solvent may be removedthrough the rapid thermal annealing method. In this way, the lightemitting efficiency of the nano-scale LED device according to thepresent invention may be improved, and defects that may occur when anelectroplating method is performed to form a metal ohmic layer inoperation 2 as will be described below may be prevented due to removalof impurities. When an ohmic layer capable of improving electricalconnectivity between both ends of the nano-scale LED device and theelectrodes and reducing contact resistance is formed in the nano-scaleLED electrode assembly manufactured by performing processes subsequentto operation 2 as will be described below without performing a rapidthermal annealing method, the ohmic layer may be poorly formed, adesired level of light emitting efficiency may not be expressed, andheavy loss of electric current may occur.

Meanwhile, the rapid thermal annealing method may be performed againbefore operation 2 or after operation 3. In this way, electricalconnectivity between the both ends of the nano-scale LED devices and theelectrodes may be further improved.

Specifically, FIG. 11 is an SEM image of a nano-scale LED electrodeassembly after performing operations 2 and 3, and FIG. 12 is an SEMimage of a nano-scale LED electrode assembly which is subjected to arapid thermal annealing method after performing operations 2 and 3.Comparing FIGS. 11 and 12, the nano-scale LED devices and the electrodesare coated with Au nanoparticles, and contact points between theelectrodes and the nano-scale LED devices are filled with the Aunanoparticles in both cases. However, it can be seen that a level of thefilling Au nanoparticles is significant in FIG. 12, compared to that inFIG. 11, as observed with the naked eye.

The rapid thermal annealing method may be performed by thermallyannealing the nano-scale LED electrode assembly at 600° C. to 1,000° C.for 0.5 to 10 minutes, preferably for 1 to 7 minutes. When the rapidthermal annealing is performed at a temperature of less than 600° C.and/or for a time of less than 0.5 minutes, impurities may not becompletely removed, and a contact reaction between the nano-scale LEDdevices and the electrodes may not occur at all. On the other hand, whenthe rapid thermal annealing is performed at a temperature of greaterthan 1,000° C. and/or for a time of greater than 10 minutes, the basesubstrate and/or the electrodes may be deformed or broken, and a voltagemay not be normally applied to the nano-scale LED devices due to anincrease in resistance.

Finally, operation 2 of the method of manufacturing a nano-scale LEDelectrode assembly including a selective metal ohmic layer according tothe present invention includes immersing the nano-scale LED electrodeassembly in an electroplating solution, and forming a metal ohmic layeron the nano-scale LED electrode assembly by applying a power source toone of the first and second electrodes of the nano-scale LED electrodeassembly to perform an electroplating process for a plating time T₁ of 1to 300 minutes, preferably 5 to 200 minutes, and more preferably 10 to55 minutes.

Operation 2 may be performed using an electroplating process. The term“electroplating process” refers to a process in which, when a powersource is applied between an anode and a cathode, an oxidation reactionoccurs at the anode and a reduction reaction occurs at the cathode sothat a material in the cathode is coated with a metal. In this case thecathode and the anode may be immersed in an electroplating solution.Here, metals to be plated onto the cathode in the electroplatingsolution may be present in an ionic state.

Specifically, operation 2 of the present invention may be performedusing the electroplating process, and thus will be described withreference to FIG. 10, as follows.

FIG. 10 is a diagram of an electroplating process performed to form ametal ohmic layer according to one preferred embodiment of the presentinvention.

First, an electrolytic bath 410 containing an electroplating solution420 is prepared. The electroplating solution 420 may include a metalprecursor in the form of an ionic compound, deionized water, and anadditive.

Next, a working electrode 440, a reference electrode 460 and a counterelectrode 450 are immersed in the electroplating solution 420. Thenano-scale LED electrode assembly according to the present invention maybe used as the working electrode 440.

Subsequently, the nano-scale LED electrode assembly of the presentinvention used as the working electrode 440, the reference electrode460, and the counter electrode 450 are electrically connected to a powersource 430. The counter electrode 450 is connected to a positive pole(+) of the power source 430, and the first electrode or second electrodeof the nano-scale LED electrode assembly according to the presentinvention is connected to a negative pole (−) of the power source 430.Thereafter, a power source is applied for a plating time T₁ of 1 to 300minutes, preferably 5 to 200 minutes, and more preferably 10 to 55minutes to deposit a metal precursor onto one surface of the nano-scaleLED electrode assembly, preferably surfaces of the plurality ofnano-scale LED devices, thereby forming a metal ohmic layer. When thepower source is applied for less than 1 minute, a metal ohmic layer maynot be sufficiently formed on one surface of the electrode line on whichthe plurality of nano-scale LED devices are self-aligned. On the otherhand, when the power source is applied for greater than 300 minutes,shorts may occur on the electrodes.

In this case, the power source 430 applied to form a superior metalohmic layer may be pulse waves having a voltage of −0.2 to −1.0 V. Here,the pulse waves of the power source may be applied for 0.05 to 30seconds, more preferably 1 to 10 seconds, and paused for 0.05 to 30seconds, more preferably 1 to 10 seconds. However, conditions forapplying/pausing such pulse waves are not limited.

When the metal ohmic layer is formed through operation 2, a metal ohmiclayer may be formed only on the first or second electrode to which thepower source 430 is electrically connected, or a first metal ohmic layermay be formed on the first and second electrodes. In the case of theformer, since a metal ohmic layer is not formed on the first or secondelectrode to which the power source 430 is not connected, operation 3may be performed to uniformly form a metal ohmic layer on the entiresurface of the electrode line.

Operation 3 may include forming a metal ohmic layer on the nano-scaleLED electrode assembly by applying a power source to a counter electrodeof the first or second electrode to which the power source is applied inoperation 2 to perform an electroplating process for a plating time T₂satisfying the following Mathematical Expression 1.1 Minute≤Plating time T ₂ ≤T ₁  [Mathematical Expression 1]

wherein T₁ represents a plating time for the electroplating process inoperation 2.

Operation 3 may be performed in the same manner in as operation 2 usingan electroplating process. Thus, the counter electrode 450 may beconnected to a positive pole (+) of the power source 430, and a counterelectrode of the first or second electrode to which the power source inoperation 2 is applied in the electrode line of the nano-scale LEDelectrode assembly according to the present invention may be connectedto a negative pole (−) of the power source 430. Thereafter, a powersource may be applied for a plating time T₂ satisfying MathematicalExpression 1 to deposit a metal precursor on one surface of thenano-scale LED electrode assembly, preferably the electrode line onwhich the plurality of nano-scale LED devices are self-aligned, therebyforming a metal ohmic layer. In this case, the power source 430 appliedto form a metal ohmic layer capable of exhibiting superior physicalproperties may be pulse waves having a voltage of −0.2 to −1.0 V. Here,the power source of pulse waves may be applied for 0.05 to 30 seconds,more preferably 1 to 10 seconds, and may be paused for 0.05 to 30seconds, more preferably 1 to 10 seconds. However, conditions forapplying/pausing such pulse waves are not limited. Also, it is desirableto perform this operation for a plating time T₂ of preferably 4 minutes,more preferably 8 minutes so as to manufacture a nano-scale LEDelectrode assembly having superior physical properties.

As described above, the metal ohmic layer may be formed by depositing ametal precursor included in the electroplating solution onto theelectrode line through a reduction reaction of the electrode line in thenano-scale LED electrode assembly. In this case, the metal ohmic layer50 may be formed on one surface of the nano-scale LED electrodeassembly, preferably surfaces of the electrode lines 110 a and 110 b onwhich the nano-scale LED devices 20 are self-aligned, as shown in FIGS.13 and 14.

As such, a reason for forming the metal ohmic layer on surfaces of theelectrode lines 110 a and 110 b on which nano-scale LED devices 20 areself-aligned is because the plurality of nano-scale LED devices 20 emitlight when the power source is applied to the first electrode 110 a andthe second electrode 110 b to which the plurality of nano-scale LEDdevices are connected. In this case, contact resistance that may occurbetween the nano-scale LED devices 20 and the first and secondelectrodes 110 a and 110 b may be reduced.

The term “contact resistance” refers to electric resistance that occurson a contact surface of two adjacent conductors when an electric currentis allowed to flow through the contact surface of the two conductors.Here, when two conductors come in contact with each other to send anelectric current, a voltage applied to a contact region between theconductors drops, causing an increase in temperature. In other words,the term “contact resistance” refers to electric resistance that occursin a contact region between the plurality of nano-scale LED devices 20and the first and second electrodes 110 a and 110 b, which are adjacentto each other, when an electric current is allowed to flow through thecontact region from the power source applied to the metal line. In thiscase, a voltage applied to the contact region drops, causing an increasein temperature.

Since the metal ohmic layer 50 is selectively formed to include acontact region between the nano-scale LED device 20 and the firstelectrode 110 a and a contact region between the nano-scale LED device20 and the second electrode 110 b, the contact between the nano-scaleLED devices 20 and the first and second electrodes 110 a and 110 b maybe improved. Also, since the metal ohmic layer 50 is formed of aconductive material, conductivity between the nano-scale LED devices 50and the first and second electrodes 110 a and 110 b may be increased,and contact resistance may also be reduced.

As described above, an additive may be included in the electroplatingsolution. In this case, a leveler for leveling the metal ohmic layer 50,a grain refiner for refining grains of the metal ohmic layer 50, astress reducer for reducing stress in the metal ohmic layer 50 while themetal ohmic layer 50 is formed on surfaces of the electrode lines 110 aand 110 b, and a wetting agent for promoting adhesion of metal elementsof a metal ionic compound to one surface of the electrode line may beused as additives.

Meanwhile, the metal precursor may include one or more selected from thegroup consisting of a gold precursor, a silver precursor, a copperprecursor, and a platinum precursor. That is, when the gold precursor isincluded in the electroplating solution, a gold material may be used toform a metal ohmic layer on one surface of the electrode line on whichthe nano-scale LED devices are self-aligned. When the silver precursoris included in the electroplating solution, a silver material may beused to form a metal ohmic layer on one surface of the electrode line onwhich the nano-scale LED devices are self-aligned.

Types of the gold precursor usable in the present invention may includeHAuCl₄, KAuCl₄, etc., types of the silver precursor may includeKAg(CN)₂, NaAg(CN)₂, AgCN, AgOCN, AgNO₃, AgCO₃, C₂H₃AgO₃, etc., andtypes of the copper precursor may include CuCN, Cu(NO₃)₂, CuCO₃,Cu₂(OAc)₄, CuSO₄, etc. Also, types of the platinum precursor may includeH₂PtCl₆, etc.

However, the metal precursor of the present invention is not limited tothe above metal precursors, and all types of metal precursors may beused as long as they can be used as a plating material in anelectroplating process.

Further, the electroplating solution may include the metal precursor ata concentration of 0.001 to 100 mM, more preferably 0.01 to 100 mM, andmost preferably 0.01 to 50 mM.

When the concentration of the metal precursor is less than 0.001 mM,insufficient deposition may occur. On the other hand, when theconcentration of the metal precursor is greater than 100 mM, excessivedeposition may occur, resulting in shorts in the nano-scale LEDelectrode assembly.

Meanwhile, operations 2 and/or 3 may be performed at a temperature of 10to 30° C., preferably a temperature of 15 to 25° C. When the temperatureis less than 10° C., the metal ohmic layer may not be sufficientlyformed. On the other hand, when the temperature is greater than 30° C.,a metal forming a metal ohmic layer may be formed in an oxidized state,and shorts may also occur in the nano-scale LED electrode assembly.

Although the present invention has been described with reference toexemplary embodiments thereto, it should be understood that thefollowing examples are merely preferred examples for the purpose ofillustration only and is not intended to limit or define the scope ofthe invention. Also, it will be apparent to those skilled in the art towhich the present invention belongs that various modifications andchanges can be made without departing from the scope of the presentinvention. For example, components specifically described in exemplaryembodiments of the present invention may be modified to implement thepresent invention. Also, it should be understood that that differencesassociated with such modifications and changes are intended to beencompassed in the scope of the present invention defined by theappended claims and their equivalents.

Hereinafter, the present invention will be described in further detailwith exemplary embodiments thereto. However, it should be understoodthat following examples are not intended to limit the scope of thepresent invention, but intended to aid in understanding the presentinvention.

Comparative Example 1

An electrode line was formed on a base substrate formed of a quartzmaterial and having a thickness of 850 μm, as shown in FIG. 2. In thiscase, in the electrode line, the width of the first electrode was 3 μm,the width of the second electrode was 3 μm, the distance between thefirst electrode and the second electrode adjacent to the first electrodewas 2 μm, and the thickness of the electrode was 0.2 μm. Also, the firstelectrode and the second electrode were formed of a material such astitanium/gold, and an area of a region in which nano-scale LED deviceswere mounted in the electrode line was 4.2×10⁷ μm².

Next, 1.0 parts by weight of nano-scale LED devices, with specificationslisted in the following Table 1 and having a structure as shown in FIG.6 and in which a portion of an active layer of each of the nano-scaleLED devices was coated with an insulating coating film as listed in thefollowing Table 1, was mixed with 100 parts by weight of acetone toprepare a dispersion solution including the nano-scale LED devices.

The prepared dispersion solution was dropped onto a region of theelectrode line, and a power source having a voltage V_(Ac) of 30 V and afrequency of 950 kHz was then applied to the electrode line for 1 minuteto manufacture a nano-scale LED assembly.

TABLE 1 Material Height (μm) Diameter (μm) First electrode layerChromium 0.03 0.6 First conductive n-GaN 1.64 0.6 semiconductor layerActive layer InGaN 0.1 0.6 Second conductive p-GaN 0.2 0.6 semiconductorlayer Second electrode Chromium 0.03 0.6 layer Insulating coating filmAluminum oxide thickness 0.02 Nano-scale LED — 2 0.62 device

Comparative Example 2

The nano-scale LED electrode assembly manufactured in ComparativeExample 1 was thermally annealed at a temperature of 810° C. for 2minutes to manufacture a nano-scale LED electrode assembly.

Example 1

An electroplating process was described with reference to FIG. 10.First, an electroplating solution 420 was injected into an electrolyticbath 410. The electroplating solution 420 was prepared at aconcentration of 0.05 mM by diluting HAuCl₄ (Sigma-Aldrich Co. LLC.,99.99% trace metals basis, 30% by weight in dilute HCl) with deionizedwater. Next, a working electrode 440, a reference electrode 460, and acounter electrode 450 were immersed in the electroplating solution 420.The nano-scale LED electrode assembly manufactured in ComparativeExample 2 was used as the working electrode 440, an Ag/AgCl electrodewas used as the reference electrode, and a Pt plate was used as thecounter electrode. Thereafter, the working electrode 440, the referenceelectrode 460 and the counter electrode 450 were electrically connectedto a power source 430. In this case, the counter electrode 450 wasconnected to a positive pole (+) of the power source 430, and a firstelectrode of the nano-scale LED electrode assembly manufactured inComparative Example 2 used as the working electrode 440 was connected toa negative pole (−) of the power source 430. Then, the power source 430was applied for 25 minutes in the form of pulse waves having a voltageof −0.2 V. One cycle of applying the power source 430 for 2 seconds andpausing the power source 430 for 2 seconds was repeated to manufacture anano-scale LED electrode assembly having a metal ohmic layer formedtherein.

Example 2

A metal plating process was performed on the nano-scale LED electrodeassembly manufactured in Example 1 in the same manner in as inExample 1. However, the counter electrode 450 was connected to apositive pole (+) of the power source 430, and a second electrode of thenano-scale LED electrode assembly manufactured in Example 1 wasconnected to a negative pole (−) of the power source 430. Thereafter,the power source 430 was applied for 25 minutes in the form of pulsewaves having a voltage of −0.2 V. One cycle of applying the power source430 for 2 seconds and pausing the power source 430 for 2 seconds wasrepeated to manufacture a nano-scale LED electrode assembly having ametal ohmic layer formed therein.

Experimental Example 1

For the nano-scale electrode assemblies manufactured in ComparativeExamples 1 and 2 and Examples 1 and 2, the nano-scale LED devicesemitting blue light were observed by applying an AC power source havinga voltage VAC of 30 V and a frequency of 950 kHz to the electrode linefor 1 minute. FIG. 15 is a blue electroluminescent image for thenano-scale electrode assembly manufactured in Comparative Example 1,FIG. 16 is a blue electroluminescent image for the nano-scale electrodeassembly manufactured in Comparative Example 2, FIG. 17 is a blueelectroluminescent image for the nano-scale electrode assembly having ametal ohmic layer formed therein manufactured in Example 1, and FIG. 18is a blue electroluminescent image for the nano-scale LED electrodeassembly having a metal ohmic layer formed therein manufactured inExample 2.

Referring to FIGS. 15 to 18, it could be seen that the blueelectroluminescence for the nano-scale electrode assembly manufacturedin Comparative Example 2 had superior light emitting efficiency to theblue electroluminescence for the nano-scale electrode assemblymanufactured in Comparative Example 1. Specifically, it could be seenthat the light emitting efficiency of the nano-scale electrode assemblymanufactured in Comparative Example 2 was approximately 3.74 times thelight emitting efficiency of the nano-scale electrode assemblymanufactured in Comparative Example 1.

Accordingly, it could be seen that acetone used as the dispersionsolvent was removed when the nano-scale electrode assembly manufacturedin Comparative Example 1 was thermally annealed, and the light emittingefficiency of the nano-scale electrode assembly was enhanced as theelectrical connectivity between the nano-scale LED devices and theelectrodes was further improved.

Also, it could be seen that the blue electroluminescence for thenano-scale electrode assembly having a metal ohmic layer formed thereinmanufactured in Example 1 had superior light emitting efficiency to theblue electroluminescence for the nano-scale electrode assembliesmanufactured in Comparative Examples 1 and 2. Specifically, it could beseen that the light emitting efficiency of the nano-scale electrodeassembly having a metal ohmic layer formed therein manufactured inExample 1 was approximately 15 times the light emitting efficiency ofthe nano-scale electrode assembly manufactured in Comparative Example 1,and approximately 4 times the light emitting efficiency of thenano-scale electrode assembly manufactured in Comparative Example 2.

Accordingly, it could be seen that, when an electroplating process wasperformed on the nano-scale electrode assembly to form a metal ohmiclayer, conductivity between the nano-scale LED devices and the electrodeline was enhanced, and contact resistance was reduced, resulting inimproved light emitting efficiency.

Finally, it could be seen that the blue electroluminescence for thenano-scale LED electrode assembly having a metal ohmic layer formedtherein manufactured in Example 2 had superior light emitting efficiencyto the blue electroluminescence for the nano-scale LED electrodeassembly having a metal ohmic layer formed therein manufactured inExample 1. Specifically, it could be seen that the light emittingefficiency of the nano-scale LED electrode assembly having a metal ohmiclayer formed therein manufactured in Example 2 was approximately 1.2times the light emitting efficiency of the nano-scale electrode assemblymanufactured in Example 1.

Accordingly, it could be seen that, when a power source was applied tothe first electrode in the electrode line, as described in Example 1, toform a metal ohmic layer, the metal ohmic layer was not formed on thesecond electrode, or the formed metal ohmic layer did not serve toreduce contact resistance between the nano-scale LED devices and thesecond electrode. Therefore, it was revealed that the light emittingefficiency of the nano-scale LED electrode assembly was able to beimproved in Example 2 when the power source was connected to the secondelectrode in the electrode line in the same manner in as in Example 1 tore-form a metal ohmic layer.

Comparative Example 3

A nano-scale LED electrode assembly was manufactured in the same manneras in Comparative Example 1, except that a green nano-scale LED deviceas detailed the following Table 2 was used instead of the nano-scale LEDdevice of Table 1.

Example 3

A nano-scale LED electrode assembly was manufactured in the same manneras in Example 2, except that a green nano-scale LED device as detailedin the following Table 2 was used instead of the nano-scale LED deviceof Table 1.

TABLE 2 Material Height (μm) Diameter (μm) First electrode layerChromium 0.15 0.50 First conductive n-GaN 4 0.50 semiconductor layerActive layer InGaN/GaN 0.2 0.50 Second conductive p-GaN 0.15 0.50semiconductor layer Second electrode Chromium 0.03 0.50 layer Insulatingcoating film Aluminum oxide thickness 0.02 Nano-scale LED — 4.53 0.52device

Experimental Example 2

The electroluminescence (EL) intensities of light emitted from thenano-scale electrode assemblies manufactured in Comparative Example 3and Example 3 were measured when a varying drive voltage ranging from 0to 21.0 V_(rms) was applied to the electrode line at a frequency of 60Hz. The results are shown in FIGS. 19 and 20.

FIG. 19 is a graph showingEL intensities of the nano-scale LED electrodeassembly manufactured in Comparative Example 3 according to the varyingdrive voltage, and FIG. 20 is a graph showing EL intensities of thenano-scale LED electrode assembly manufactured in Example 3 according tothe varying drive voltage.

Specifically, referring to FIG. 19, it could be seen that green lightwas emitted in a minimum voltage range of 4.0 to 5.5 V_(rms), but thatgreen light was also emitted in a voltage range 2.8 to 3.5 V_(rms),which is significantly lower than the minimum voltage range as shown inFIG. 20. Therefore, it was revealed that the contact resistance wassignificantly reduced and the electrical connectivity of an electricalcontact region was significantly increased due to the rapid thermalannealing process and the formation of the metal ohmic layer. Also, itwas revealed that the electroluminescence intensity which increased withan increasing voltage was significantly higher in the nano-scale LEDelectrode assembly as shown in FIG. 20, compared to that of thenano-scale LED electrode assembly as shown in FIG. 19. Specifically, itwas revealed that the electroluminescence intensity at 21.0 V_(rms)increased approximately 371 times.

Meanwhile, FIGS. 21 and 22 are images of the nano-scale LED electrodeassemblies manufactured in Comparative Example 3 and Example 3 whichemit light when an AC power source having a voltage of 21.0 V_(rms) isapplied to the nano-scale LED electrode assemblies at a frequency of 60Hz, respectively. As observed on the images with the naked eye, it couldbe seen that, even when the nano-scale LED devices were self-aligned onthe electrode without performing a rapid thermal annealing process toincrease an electrical connection or forming a selective ohmic layer,the nano-scale LED devices were connected to the electrode so that thelight emission was observed with the naked eye, as shown in FIG. 21.However, it was revealed that a level of light emission wassignificantly higher in FIG. 22, compared to the level of light emissionas shown in FIG. 21. From these results, it was expected that thecontact resistance significantly decreased and the electricalconnectivity significantly increased when the rapid thermal annealingprocess and the formation of the selective ohmic layer were performed atthe same time.

The method of manufacturing a nano-scale LED electrode assemblyaccording to the present invention can be useful in increasingconductivity between an LED device and electrodes and also reducingcontact resistance therebetween by depositing a conductive material in aregion in which the LED device comes in contact with the electrodes soas to improve the contact between the LED device and the electrodes,thereby further improving light extraction efficiency of the LED device.

It will be apparent to those skilled in the art that variousmodifications can be made to the above-described exemplary embodimentsof the present invention without departing from the scope of theinvention. Thus, it is intended that the present invention covers allsuch modifications provided they come within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A method of manufacturing a nano-scale LEDelectrode assembly comprising a selective metal ohmic layer, comprising:(1) manufacturing a nano-scale LED electrode assembly by self-aligningnano-scale LED devices on an electrode line comprising first and secondelectrodes which are formed on a base substrate to be spaced apart fromeach other; (2) forming a metal ohmic layer on the nano-scale LEDelectrode assembly at least including a contact region betweennano-scale LED device and electrode line by immersing the nano-scale LEDelectrode assembly in an electroplating solution and applying a powersource to one of the first and second electrodes of the nano-scale LEDelectrode assembly to perform an electroplating process for a platingtime (T₁) of 1 to 300 minutes; and (3) forming a metal ohmic layer onthe nano-scale LED electrode assembly by applying a power source to theother electrode, to which the power source is not applied in operation2, to perform an electroplating process for a plating time T2 satisfyingthe following Mathematical Expression 1:1 Minute≤plating time (T ₂)≤T ₁  [Mathematical Expression 1] wherein T₁represents a plating time required for the electroplating process inoperation
 2. 2. The method of claim 1, wherein the power source inoperation 2 is applied in the form of pulse waves having a voltage of−0.2 to −1.0 V, and the power source of the pulse waves is applied for0.05 to 30 seconds and paused for 0.05 to 30 seconds.
 3. The method ofclaim 2, wherein the power source in operation 3 is applied in the formof pulse waves having a voltage of −0.2 to −1.0 V, and the power sourceof the pulse waves is applied for 0.05 to 30 seconds and paused for 0.05to 30 seconds.
 4. The method of claim 1, wherein the electroplatingsolution comprises at least one metal precursor selected from the groupconsisting of a gold precursor, a silver precursor, a copper precursor,and a platinum precursor metal precursor selected from the groupconsisting of a gold precursor, a silver precursor, a copper precursor,and a platinum precursor.
 5. The method of claim 4, wherein theelectroplating solution comprises the metal precursor at a concentrationof 0.001 to 100 mM.
 6. The method of claim 1, wherein operation 1comprises: 1-1) injecting a dispersion solution comprising a dispersionsolvent and nano-scale LED devices toward one surface of the basesubstrate on which the electrode line comprising the first and secondelectrodes spaced apart from each other is formed; and 1-2)manufacturing the nano-scale LED electrode assembly by applying thepower source to the electrode line to self-align the nano-scale LEDdevices, wherein the manufactured nano-scale LED electrode assembly isthermally annealed at 600° C. to 1,000° C. for 0.5 to 10 minutes.
 7. Themethod of claim 1, wherein operation 1 includes either spirally orinterdigitatedly disposing the first and second electrodes to be spacedapart from each other.
 8. The method of claim 1, wherein each of thenano-scale LED devices comprises a first electrode layer; a firstconductive semiconductor layer formed on the first electrode layer; anactive layer formed on the first conductive semiconductor layer; asecond conductive semiconductor layer formed on the active layer; and asecond electrode layer formed on the second conductive semiconductorlayer, and each of the nano-scale LED devices further comprises aninsulating coating film which coats an outer surface thereof.
 9. Themethod of claim 8, wherein the insulating coating film is applied tocover the entire outer surface of the active layer.
 10. The method ofclaim 9, wherein outer surfaces of the first and second electrode layersof the nano-scale LED devices are not coated with the insulating coatingfilm.
 11. The method of claim 1, wherein the plating time (T1) inoperation 2 is in a range of 10 to 55 minutes.
 12. The method of claim8, wherein a width X of the first electrode, a width Y of the secondelectrode, a distance Z between the first electrode and the secondelectrode adjacent to the first electrode, and a height H of thenano-scale LED devices satisfy the following Relation 1:0.5Z≤H<X+Y+2Z  [Relation 1] wherein 100 nm<X≤10 μm, 100 nm<Y≤10 μm, and100 nm<Z≤10 μm.
 13. The method of claim 1, wherein operation 1 furthercomprises forming an insulating barrier on the base substrate tosurround a region of the electrode line on which the plurality ofnano-scale LED devices are positioned.
 14. The method of claim 1,wherein, after operation 3, the manufactured nano-scale LED electrodeassembly is thermally re-annealed at 600° C. to 1,000° C. for 0.5 to 10minutes.